The primary concern is to understand integration of viral DNA. With E. coli phage lambda we will determine whether the cut at the attachment site consists of two single strand breaks adjacent to a single base pair or displaced so as to generate complementary short single strands. This will be done by isolating from infected cells lambda DNA which is inverted - i.e., the natural DNA ends in the center and the two components of the attachment site being at the termini. We will also examine the structure of integrated animal viral DNA in the DNA of transformed eukaryote cells. This will be done by hybridizing viral mRNA with denatured animal DNA, isolating the RNA-DNA hybrid and studying the hybrid by electron microscopy.